pps: pps-gpio PPS ECHO implementation

This patch implements the PPS ECHO functionality for pps-gpio, that
sysfs claims is available already.

Configuration is done via device tree bindings.

No changes are made to userspace interfaces.

This patch was originally written by Lukas Senger as part of a masters
thesis project and modified for inclusion into the linux kernel by Tom
Burkart.

Link: http://lkml.kernel.org/r/20190324043305.6627-4-tom@aussec.comSigned-off-by: Tom Burkart <tom@aussec.com>
Acked-by: Rodolfo Giometti <giometti@enneenne.com>
Signed-off-by: Lukas Senger <lukas@fridolin.com>
Cc: Philipp Zabel <philipp.zabel@gmail.com>
Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/pps/clients/pps-gpio.c

@@ -35,6 +35,8 @@
 #include <linux/list.h>
 #include <linux/of_device.h>
 #include <linux/of_gpio.h>
+#include <linux/timer.h>
+#include <linux/jiffies.h>
 
 /* Info for each registered platform device */
 struct pps_gpio_device_data {
@@ -42,8 +44,12 @@ struct pps_gpio_device_data {
 	struct pps_device *pps;		/* PPS source device */
 	struct pps_source_info info;	/* PPS source information */
 	struct gpio_desc *gpio_pin;	/* GPIO port descriptors */
+	struct gpio_desc *echo_pin;
+	struct timer_list echo_timer;	/* timer to reset echo active state */
 	bool assert_falling_edge;
 	bool capture_clear;
+	unsigned int echo_active_ms;	/* PPS echo active duration */
+	unsigned long echo_timeout;	/* timer timeout value in jiffies */
 };
 
 /*
@@ -64,19 +70,56 @@ static irqreturn_t pps_gpio_irq_handler(int irq, void *data)
 	rising_edge = gpiod_get_value(info->gpio_pin);
 	if ((rising_edge && !info->assert_falling_edge) ||
 			(!rising_edge && info->assert_falling_edge))
-		pps_event(info->pps, &ts, PPS_CAPTUREASSERT, NULL);
+		pps_event(info->pps, &ts, PPS_CAPTUREASSERT, data);
 	else if (info->capture_clear &&
 			((rising_edge && info->assert_falling_edge) ||
 			(!rising_edge && !info->assert_falling_edge)))
-		pps_event(info->pps, &ts, PPS_CAPTURECLEAR, NULL);
+		pps_event(info->pps, &ts, PPS_CAPTURECLEAR, data);
 
 	return IRQ_HANDLED;
 }
 
+/* This function will only be called when an ECHO GPIO is defined */
+static void pps_gpio_echo(struct pps_device *pps, int event, void *data)
+{
+	/* add_timer() needs to write into info->echo_timer */
+	struct pps_gpio_device_data *info = data;
+
+	switch (event) {
+	case PPS_CAPTUREASSERT:
+		if (pps->params.mode & PPS_ECHOASSERT)
+			gpiod_set_value(info->echo_pin, 1);
+		break;
+
+	case PPS_CAPTURECLEAR:
+		if (pps->params.mode & PPS_ECHOCLEAR)
+			gpiod_set_value(info->echo_pin, 1);
+		break;
+	}
+
+	/* fire the timer */
+	if (info->pps->params.mode & (PPS_ECHOASSERT | PPS_ECHOCLEAR)) {
+		info->echo_timer.expires = jiffies + info->echo_timeout;
+		add_timer(&info->echo_timer);
+	}
+}
+
+/* Timer callback to reset the echo pin to the inactive state */
+static void pps_gpio_echo_timer_callback(struct timer_list *t)
+{
+	const struct pps_gpio_device_data *info;
+
+	info = from_timer(info, t, echo_timer);
+
+	gpiod_set_value(info->echo_pin, 0);
+}
+
 static int pps_gpio_setup(struct platform_device *pdev)
 {
 	struct pps_gpio_device_data *data = platform_get_drvdata(pdev);
 	struct device_node *np = pdev->dev.of_node;
+	int ret;
+	u32 value;
 
 	data->gpio_pin = devm_gpiod_get(&pdev->dev,
 		NULL,	/* request "gpios" */
@@ -87,6 +130,33 @@ static int pps_gpio_setup(struct platform_device *pdev)
 		return PTR_ERR(data->gpio_pin);
 	}
 
+	data->echo_pin = devm_gpiod_get_optional(&pdev->dev,
+			"echo",
+			GPIOD_OUT_LOW);
+	if (data->echo_pin) {
+		if (IS_ERR(data->echo_pin)) {
+			dev_err(&pdev->dev, "failed to request ECHO GPIO\n");
+			return PTR_ERR(data->echo_pin);
+		}
+
+		ret = of_property_read_u32(np,
+			"echo-active-ms",
+			&value);
+		if (ret) {
+			dev_err(&pdev->dev,
+				"failed to get echo-active-ms from OF\n");
+			return ret;
+		}
+		data->echo_active_ms = value;
+		/* sanity check on echo_active_ms */
+		if (!data->echo_active_ms || data->echo_active_ms > 999) {
+			dev_err(&pdev->dev,
+				"echo-active-ms: %u - bad value from OF\n",
+				data->echo_active_ms);
+			return -EINVAL;
+		}
+	}
+
 	if (of_property_read_bool(np, "assert-falling-edge"))
 		data->assert_falling_edge = true;
 	return 0;
@@ -122,9 +192,11 @@ static int pps_gpio_probe(struct platform_device *pdev)
 	/* GPIO setup */
 	if (pdata) {
 		data->gpio_pin = pdata->gpio_pin;
+		data->echo_pin = pdata->echo_pin;
 
 		data->assert_falling_edge = pdata->assert_falling_edge;
 		data->capture_clear = pdata->capture_clear;
+		data->echo_active_ms = pdata->echo_active_ms;
 	} else {
 		ret = pps_gpio_setup(pdev);
 		if (ret)
@@ -148,6 +220,11 @@ static int pps_gpio_probe(struct platform_device *pdev)
 	data->info.owner = THIS_MODULE;
 	snprintf(data->info.name, PPS_MAX_NAME_LEN - 1, "%s.%d",
 		 pdev->name, pdev->id);
+	if (data->echo_pin) {
+		data->info.echo = pps_gpio_echo;
+		data->echo_timeout = msecs_to_jiffies(data->echo_active_ms);
+		timer_setup(&data->echo_timer, pps_gpio_echo_timer_callback, 0);
+	}
 
 	/* register PPS source */
 	pps_default_params = PPS_CAPTUREASSERT | PPS_OFFSETASSERT;
@@ -180,6 +257,11 @@ static int pps_gpio_remove(struct platform_device *pdev)
 	struct pps_gpio_device_data *data = platform_get_drvdata(pdev);
 
 	pps_unregister_source(data->pps);
+	if (data->echo_pin) {
+		del_timer_sync(&data->echo_timer);
+		/* reset echo pin in any case */
+		gpiod_set_value(data->echo_pin, 0);
+	}
 	dev_info(&pdev->dev, "removed IRQ %d as PPS source\n", data->irq);
 	return 0;
 }
@@ -204,4 +286,4 @@ MODULE_AUTHOR("Ricardo Martins <rasm@fe.up.pt>");
 MODULE_AUTHOR("James Nuss <jamesnuss@nanometrics.ca>");
 MODULE_DESCRIPTION("Use GPIO pin as PPS source");
 MODULE_LICENSE("GPL");
-MODULE_VERSION("1.1.0");
+MODULE_VERSION("1.2.0");

include/linux/pps-gpio.h

@@ -24,8 +24,10 @@
 
 struct pps_gpio_platform_data {
 	struct gpio_desc *gpio_pin;
+	struct gpio_desc *echo_pin;
 	bool assert_falling_edge;
 	bool capture_clear;
+	unsigned int echo_active_ms;
 };
 
 #endif /* _PPS_GPIO_H */